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4 Defining the Test Configuration

4 Defining the Test Configuration

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3.4.2 Configuration Test

Differential protection relays are usually set to be very sensitive. Therefore, even small differential currents

will lead to a trip. If the wiring is incorrect or if parameters such as the nominal voltages, the zero sequence

elimination, the CT ratios or the CT star-point directions are not set correctly, currents flowing through the

protected area may lead to an unwanted operation. The configuration test simulates external faults with fault

currents flowing through the protected area. During these faults the relay must not trip and therefore, this

test confirms that the wiring, as well as the above mentioned parameters, are correct.

General

General settings of the test are entered in this tab.

1.



1



2.

3.



2

3



4



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4.



This setting defines on which side of the transformer the fault

and the source should be located for the fault simulation.

The test time should be set long enough to allow the

measured currents from the relay to be read.

These settings define if the CMC should generate voltages

and whether the test should be time synchronized via GPS

or IRIG-B. In this example neither of these will be necessary.

The Trigger Logic has to be defined according to the relay

configuration.

Note: If the relay uses multiple trip contacts, they should be

linked with OR. This way the test will be assessed as failed if

any of the trip contacts are triggered.



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Test Data

In this tab the test points can be entered.



1

2



4



3



1.

2.

3.



Enter the test current and click Add to set a test point. The test current will be relative to the nominal

current of the fault side.

The new test point appears in the test point list.

The fault type can be defined with this setting.

Note: Only one fault type can be set per test module. Add more test modules to the OCC file, if multiple

fault types are to be tested.



4.



The current outputs of the CMC are shown in the single line view.



© OMICRON 2013



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Test

This tab is used to assess and document the test.

1.



1



2.



2



3.

4.



3



Note:



4



Define whether you want to enter the measured phase

currents or the calculated differential and bias currents. For

most of the digital differential relays the option

Idiff and Ibias is the easiest way to assess the relay

behavior.

Start the test by clicking the Start/continue test button on

the toolbar.

This activates the input fields for the measured currents.

Now the measured currents can be read from the relay and

entered here. It should be kept in mind that the current

output will be stopped after the test time is elapsed.

The test current and the status of the test are displayed

here.

The test can be assessed with this option. If a trip occurs

during the test time, the test will automatically be assessed

as failed.



To test the numerical zero sequence elimination, it is recommended that at least one phase-toground fault is placed at the grounded side of the transformer.

In order to assess the test, the differential and bias currents that should be measured by the

relay must be calculated. The necessary formulae can be obtained from the relay manual. If

these theoretically calculated currents match the currents read out from the relay, the test can

be assessed as passed. During the test the differential current must be zero in each phase.



© OMICRON 2013



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3.4.3 Operating Characteristic Test

This test confirms the operating characteristic of the differential relay. Test shots are placed in the operating

characteristic diagram and if they are above the operating characteristic, the relay must trip. If they are below

the characteristic the relay must not trip.

General

General settings of the test are entered in this tab.

1.



1

2.



2



3.



4.



3

5.



4



If this option remains unselected, a search test will

only search within the specified tolerances.

If, however, this option is selected, the search test will

also search outside of the tolerance band. In this case

the test will always be assessed as passed.

A pre-fault current can be applied before each test

shot.

This setting activates a voltage output during the test.

In this example it is not necessary to select the

voltage output.

Select this option if the test should be time

synchronized via GPS or IRIG-B.

For the operating characteristic test, the Trigger Logic

has to be defined according to the relay configuration.

Note: If the relay uses multiple trip contacts, they

should be linked with AND. This way a test shot will

only be assessed as tripped if all of the trip contacts

are triggered.



5



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Shot Test



With the shot test, test shots can be placed in the operating characteristic diagram. This can be done by

clicking the operating characteristic diagram and then clicking Add to set the previously clicked test shot.

Alternatively, the test shots can be set by entering the currents Idiff and Ibias manually.

To test the operating characteristic, test shots can be placed above and below the operating characteristic

outside the tolerance band. In order to confirm that the operating characteristic is within the specified

tolerances, it is recommended that test shot pairs are placed close to the boundary of the tolerance band.



© OMICRON 2013



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Search Test



With the search test, vertical search lines can be added by clicking the operating characteristic diagram and

then clicking Add or by manually entering the current Ibias of the search line. The test module will

automatically place test shots along this line to search for the exact position of the operating characteristic.

With the search test, the exact position of the operating characteristic can be found, whereas with the shot

test, it can be quickly confirmed whether the operating characteristic is within the specified tolerance band.

Note:



It is not possible to do a shot test and a search test in the same test module. Remove all test

shots before adding search lines or vice versa.

Only one fault type can be set per test module. If multiple fault types are to be tested, more test

modules can be added to the OCC file.

When testing the operating characteristic it is recommended that each line segment is tested at

two different positions (if possible). These test positions should not be too close to each other

and also not too close to the corner points of the operating characteristic. This ensures that the

characteristic settings are assessed properly.



© OMICRON 2013



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3.4.4 Trip Times Test

This test confirms the trip times of the differential protection function. Therefore, test shots with different

differential currents are applied to measure the corresponding trip times.

Factors

1.



1

2.



Select Use evaluation factors to overwrite the test object

tolerances. The new tolerances can be entered below as

Diff Current Factors and Diff Time Factors. In this example

it is not necessary to select this function.

This setting activates a voltage output during the test. In this

example it is not necessary to select the voltage output.



2



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General



1



2

2

3



1.

2.



3.



A pre-fault current can be applied before each test shot.

This setting defines the slope of the test line. The resulting test line is also shown in the operating

characteristic diagram. All the test shots in this test module will be placed on this line. Therefore, it is

advantageous to have not more than one intersection with the operating characteristic. For the majority of

differential relays this setting can remain at the default value.

For the trip times test, the Trigger Logic has to be defined according to the relay configuration.

Note: If the relay uses multiple trip contacts, they should be linked with AND. This way a test shot will

only be assessed as tripped if all of the trip contacts are triggered.



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Test



2

1



In the test tab the test shots are defined. To place a new test shot, either click on the trip time test plane (1)

or enter the differential current manually (2) and then click Add.

Note:



Only one fault type can be set per test module. If multiple fault types are to be tested, more test

modules can be added to the OCC file.

In order to test the trip time settings of the relay, it is recommended that one test shot is placed

above Idiff> and one above Idiff>> (Test Object parameters). This ensures that the trip times

corresponding to each differential current element are tested.



© OMICRON 2013



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3.4.5 Inrush Blocking Test

This test confirms the operation of the inrush blocking function. The test module generates differential

currents which contain harmonics which allows the inrush blocking characteristic to be tested.

General

1.



1



Select this option to apply a post-fault after each test shot. During

the post-fault period, only fundamental frequency currents without

harmonics will be generated.

Note: If the relay trips during the post-fault, the test will be

assessed as passed.



2

2.



3



3.



This setting activates a voltage output during the test. In this

example it is not necessary to select this function.

For the inrush blocking test, the Trigger Logic has to be defined

according to the relay configuration.

Note: If the relay uses multiple trip contacts, they should be

linked with OR. This way a test shot will only be assessed as

blocked if none of the trip contacts are triggered.



© OMICRON 2013



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Shot Test



2

1



4

3



The shot test applies test shots to the harmonic restraint test plane. This plane shows the harmonic blocking

characteristic with the differential current and the percentage of the harmonic current.

1.

2.

3.

4.



To set a new test shot click the test plane and then click Add.

The differential current and the harmonic percentage can also be entered manually and then Add is

clicked to define the test shot.

This option is used to define the number of the harmonic that should be tested. For the inrush blocking in

this example, this will be the second harmonic.

The fault type can be defined with this setting.

Note: Only one test phase can be set per test module. If different phases are to be tested, more test

modules can be added to the OCC file.



© OMICRON 2013



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